Engine intake air system including CAC bypass and separate bypass heater, and high-efficiency spark-ignited direct injection liquid propane engine architectures including same

ABSTRACT

An intake air circuit is structured to transmit intake air from a turbocharger compressor to an intake manifold of an engine. A charge air cooler (“CAC”), a bypass line, and a bypass heater are each positioned along the intake air circuit in parallel with each other. A first control valve is structured to controllably divert the intake air around the CAC. A second control valve is structured to controllably divert the intake air around at least one of the bypass line and the bypass heater. A controller operatively coupled to each of the engine, and the first and second control valves is structured to control each of the first and second control valves to cause the intake air to flow along a determined desired flow path based on each of measured ambient temperature and measured engine load.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is the U.S. National Stage of PCT Application No.PCT/US2018/023609, filed Mar. 21, 2018, which claims priority to and thebenefit of U.S. Provisional Patent Application No. 62/479,545, filed onMar. 31, 2017, the contents of which are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to internal combustion enginesystems.

BACKGROUND

Internal combustion engines generate motive power by burning fuel withair inside of a combustion chamber to produce work. Engines can bestructured to initiate combustion of the air-fuel mixture via sparkignition (“SI”) or compression ignition (“CI”) systems. SI enginestypically operate using gasoline, while CI engines typically operateusing diesel fuel.

However, some engines operate using alternative fuels, such as liquefiedpetroleum gas (“LPG”), natural gas, hydrogen, methane, methanol, andethanol, among other fuels. Several factors have increased interest inalternative fuels in recent years. For example, certain alternativefuels may provide improved performance over gasoline or diesel fuelregarding generated emissions, cost, long-term sustainability, and otherfactors.

LPG is a low pressure liquefied gas mixture composed primarily ofpropane and butane, and is also referred to as “liquefied propane gas”or simply “propane.” LPG has a lower carbon content than gasoline anddiesel fuel, and therefore produces less carbon dioxide (CO₂) duringcombustion. LPG also has a relatively high octane value, which can alsoresult in less CO₂ production when LPG is burned in an engine with ahigher compression ratio or at better combustion phasing than a typicalSI engine designed for a fuel such as gasoline.

Natural gas is composed primarily of methane (CH₄). Natural gas isstored either in gas form as compressed natural gas (“CNG”) or in liquidform as liquid natural gas (“LNG”). Natural gas also has a lower carboncontent and a higher octane value than gasoline and diesel fuel, andtherefore also produces less CO₂ during combustion.

SUMMARY

One example embodiment relates to an intake air system. An exampleintake air system includes a turbocharger that includes a compressor. Anintake air circuit is structured to transmit intake air from thecompressor to an intake manifold of an engine. A charge air cooler ispositioned along the intake air circuit. A bypass line is positionedalong the intake air circuit in parallel with the charge air cooler. Abypass heater is positioned along the intake air circuit in parallelwith each of the charge air cooler and the bypass line. A first valve ispositioned along the intake air circuit upstream of the charge aircooler. The first valve is structured to controllably divert the intakeair around the charge air cooler. A second valve is positioned along theintake air circuit upstream of the bypass heater. The second valve isstructured to controllably divert the intake air around at least one ofthe bypass line and the bypass heater.

In particular implementations, the first valve is a first control valve,and the second valve is a second control valve. Additionally, acontroller is operatively coupled to each of the engine, the firstcontrol valve, and the second control valve. The controller comprises anoperating conditions circuit structured to receive an engine load signalindicative of an engine load on the engine, and receive an ambienttemperature signal indicative of a measured ambient temperature externalto the engine. The controller further comprises an intake air flow pathcircuit structured to determine, based on each of the engine load signaland the ambient temperature signal, a desired flow path of the intakeair through at least one of the charge air cooler, the bypass line, andthe bypass heater. The controller still further comprises a controlvalve actuation circuit structured to control each of the first andsecond control valves to cause the intake air to flow along thedetermined desired flow path.

Various other embodiments related to a method. The method comprisesproviding an intake air system for an engine. The air intake systemcomprises an intake air circuit structured to transmit intake air fromthe compressor to an intake manifold of an engine. The air intake systemfurther comprises a charge air cooler positioned along the intake aircircuit. The air intake system still further comprises a first bypassline positioned along the intake air circuit in parallel with the chargeair cooler, and a second bypass line positioned along the intake aircircuit in parallel with each of the charge air cooler and the bypassline. The second bypass line includes a bypass heater. The methodfurther comprises selectively directing intake air flow through at leastone of the charge air cooler, the first bypass line, and the secondbypass line so as to maintain a temperature of the intake air flow abovea dew point temperature.

Various other embodiments relate to a spark-ignited liquid propane gasengine system. An example system includes a spark-ignited internalcombustion engine structured to operate using liquid propane gas as itssole fuel source. An air handling system is operatively coupled to theengine. The air handling system includes a first turbocharger, whichincludes a first turbine in exhaust gas receiving communication with afirst exhaust manifold of the engine. The first turbocharger alsoincludes a first compressor in intake air providing communication withan intake air circuit. A second turbocharger includes a second turbinein exhaust gas receiving communication with a second exhaust manifold ofthe engine, and a second compressor in intake air providingcommunication with the intake air circuit. A charge air condensationreduction system includes a charge air cooler, a bypass line, and abypass heater. Each of the charge air cooler, the bypass line, and thebypass heater is positioned along the intake air circuit in parallelwith the others. An intake air flow control system is structured tocontrollably direct intake air flow through a flow path comprising oneor more of the charge air cooler, the bypass line, and the bypass heaterin order to minimize condensation in the intake air circuit. The intakeair circuit is structured to transmit the intake air from the charge aircondensation reduction system to an intake manifold of the engine.

Various other embodiments relate to a spark-ignited liquid propane fuelengine system. An example system includes a spark-ignited internalcombustion engine structured to operate using liquid propane fuel as itssole fuel source. A direct fuel injection system is in liquid propanefuel providing communication with each of a plurality of cylinders ofthe engine. A turbocharger includes a turbine that is in exhaust gasreceiving communication with an exhaust manifold of the engine. Acompressor of the turbine is in intake air providing communication withan intake manifold of the engine.

These and other features, together with the organization and manner ofoperation thereof, will become apparent from the following detaileddescription when taken in conjunction with the accompanying drawings,wherein like elements have like numerals throughout the several drawingsdescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,aspects, and advantages of the disclosure will become apparent from thedescription, the drawings, and the claims.

FIG. 1 is a schematic diagram of an engine system including an engine, aturbocharger, and an intake air system, according to an exampleembodiment.

FIG. 2 is a block diagram of a controller of the engine system of FIG.1.

FIG. 3 is a block diagram of a high-efficiency SI LPG engine system,according to an example embodiment.

FIG. 4 is a block diagram of a high-efficiency SI LPG engine systemincluding the engine of the engine system of FIG. 3, according to analternative example embodiment.

It will be recognized that some or all of the figures are schematicrepresentations for purposes of illustration. The figures are providedfor the purpose of illustrating one or more implementations with theexplicit understanding that they will not be used to limit the scope orthe meaning of the claims.

DETAILED DESCRIPTION

Internal combustion engines are conventionally designed to be optimizedfor operation with either gasoline or diesel fuel. Because gasoline anddiesel engines far outnumber alternative fuel engines, alternative fuelengines typically comprise conventional gasoline or diesel enginesmodified to operate using alternative fuels. However, alternative fuels(e.g., propane and natural gas) typically do not have a cetane valuesufficient to allow for their ignition through compression. Accordingly,CI (e.g., diesel) engines must be converted to operate as SI engines inorder to use gaseous fuels. For example, such conversions may involvereplacing cylinder heads, pistons, fuel injection systems, etc.Alternatively, SI (e.g., gasoline) engines may be converted to operateusing gaseous fuels. However, production gasoline engines are notcapable of operating at high compression ratios, such as 11.0:1 orgreater, or 13.0:1 or greater, depending on the engine. As will beappreciated, in certain implementations, it is desirable to operate SIliquid propane fuel engines at these compression ratios.

Certain components of engines converted for use with gaseous fuels areover-sized or under-sized, because they were originally designed for usewith different fuels. For example, natural gas engines may be “stuck”with oversized original equipment manufacturer (“OEM”) charge aircoolers (“CACs”) that are sized for maximum cooling requirements ofdiesel engines. CACs are used to cool intake air in order to increasecharge density, thereby increasing power output of the engine andpreventing knock (pre-detonation of the air-fuel charge). Cooling intakeair temperature via a CAC can also reduce fuel consumption andemissions. CACs are often used with forced induction (e.g., turbochargedor supercharged) engine systems to remove heat generated by compressingthe intake air.

CACs designed for use with diesel engines operate with approximately100% efficiency when used with natural gas engines. In other words, thetemperature of air exiting the CAC is typically approximately equal tothe ambient air temperature. However, condensate may form in the CAC ifthe intake air is cooled below the dew point of water. By operating atapproximately 100% CAC efficiency, low ambient temperatures can furthercool intake air and cause condensation. For example, condensation canoccur frequently during cold weather periods, such as fall through latespring.

In some natural gas engine systems, turbochargers are structured tooperate only above a threshold engine load level. In other words, theturbocharger compressor does not generate boost pressure until theengine load exceeds a threshold value (e.g., 600 ft-lbs of torque).Accordingly, the engine operates as a “naturally aspirated” engine belowthe threshold engine load value. In this case, the turbochargercompressor may not generate enough heat to avoid condensation atlight-load and part-load operating conditions.

Some intake air systems include a CAC bypass heater to minimize intakecondensation. However, including a heater in a CAC bypass line causes asignificant air flow restriction through the bypass line. In somesituations, this airflow restriction is acceptable only when the CACbypass circuit is utilized in light engine load conditions (e.g., atidle). However, the airflow restriction is more pronounced—and in somecases unacceptable—during higher engine load operating conditions whenthe mass flow rate of the intake air is higher. Other intake air systemsinclude a CAC bypass line without a heater to minimize intakecondensation without causing significant flow restrictions. However,such systems may still result in intake condensation at low ambienttemperatures and low engine load operating conditions.

Various embodiments relate to an engine intake air system including acharge air cooler bypass and separate bypass heater. In someembodiments, the engine intake air system is structured for use withalternative fuel (e.g., natural gas or propane) engines. The intake airsystem includes an intake air circuit comprising a CAC, a CAC bypassline, and a CAC bypass heater, each being positioned along the intakeair circuit in parallel with each other. A controller is structured tooperate first and second control valves to controllably direct intakeair flow through a flow path comprising one or more of the CAC, the CACbypass line, and the CAC bypass heater, in order to minimize or preventcondensation in the intake air system. The intake air flow path isdefined based on at least engine load and ambient temperature. As willbe appreciated, the intake air system is structured to prevent intakeair condensation while minimizing airflow restrictions based at least inpart on ambient temperature and engine load.

As will be appreciated, the intake air system, according to variousembodiments, provides improved operation compared to existing intake airsystems by controllably directing intake air flow through the CAC bypassheater at light load conditions (when flow restrictions are notcritical), and through the low-restriction CAC bypass at partial loadconditions to avoid flow losses when the intake air mass flow rate ishigher. Accordingly, the present intake air system provides technicaladvantages over existing intake air systems by utilizing a hybrid CACbypass structure including a CAC bypass and a separate bypass heater inorder to minimize intake air flow restriction losses, while stillpreventing condensation of the intake air.

Various other embodiments relate to a direct injection (“DI”)turbocharged SI engine structured to operate using liquid propane fuel.For example, some embodiments relate to a DI turbocharged SI enginestructured to operate using liquid propane gas, as its sole fuel source.In some embodiments, the DI turbocharged SI liquid propane fuel engineis structured to operate using a compression ratio that is higher than11.0:1. In some embodiments, the DI turbocharged SI liquid propane fuelengine is structured to operate using a compression ratio that is higherthan 13.0:1. Operation at such compression ratios provides improvedengine efficiency. It also allows the engine to be sized smaller than aconventional engine with the same power output. Because the engine isdownsized, the engine is structured to operate at higher loads for agreater percentage of time.

In some embodiments, an operating constraint of the DI turbocharged SIliquid propane fuel engine is combustion knock due to at least in partto operation at high compression ratios. According to variousembodiments, the DI turbocharged SI liquid propane fuel engine includesone or more features to minimize or prevent engine knock. For example,in some embodiments, the DI turbocharged SI liquid propane fuel engineincludes one or more of (1) an exhaust gas recirculation (“EGR”) system;(2) a CAC; (3) a split exhaust manifold and a turbocharger with adivided (also referred to as split-entry) turbine housing; and (4)piston cooling nozzles (“PCNs”) to minimize or prevent engine knock.

FIG. 1 is a schematic diagram of an engine system 100 including anengine 102, a turbocharger 104, and an intake air system 106, accordingto an example embodiment. According to various embodiments, the engine102 is structured to be powered using an alternative fuel other thandiesel or gasoline. In some embodiments, the engine 102 is powered usinga gaseous fuel. It should be understood that, as used herein, the term“gaseous fuel” is intended to include fuels such as LPG, propane,natural gas, and other fuels, which may be stored under pressure,pumped, and injected in liquid form. In one embodiment, the engine 102is powered using propane (e.g., LPG). In another embodiment, the engine102 is powered using natural gas (e.g., CNG or LNG). However, in otherembodiments, the engine 102 is similarly powered using other types offuels.

In some embodiments, the engine 102 is originally designed to be poweredusing propane and/or natural gas. In other embodiments, however, theengine 102 is originally designed to be powered using diesel orgasoline, and is later converted to use propane and/or natural gas. Insome embodiments, the engine 102 operates as a prime mover for avehicle. In other embodiments, the engine 102 operates as a prime moverfor an electric power generator.

The engine 102 includes an intake manifold 108 and an exhaust manifold110. The intake manifold 108 is fluidly and operatively coupled to theintake air system 106. The intake manifold 108 is structured to transmitintake air received from the intake air system 106 to cylinders of theengine 102. The exhaust manifold 110 is structured to retrieve exhaustgas from the cylinders after the air/fuel mixture is combusted, and totransmit the exhaust gas to an exhaust system (not shown) foraftertreatment. In some embodiments, the engine 102 includes PCNs tocool the pistons, which operates to minimize or prevent combustionknock.

The turbocharger 104 includes a turbine 112 and a compressor 114, whichare mounted on a common shaft (not shown). The turbine 112 is in exhaustgas receiving communication with the exhaust manifold 110. The exhaustgas received from the exhaust manifold 110 causes rotation of theturbine 112, which in turn causes rotation of the compressor 114. Thecompressor 114 receives filtered fresh intake air and compresses theintake air to increase its charge density. The compressor 114 providesthe compressed intake air to the intake air system 106.

The intake air system 106 comprises an intake air circuit 116 defines aflow path for transmission of intake air from the compressor 114 to theintake manifold 108. It should be understood that the intake air circuit116 comprises conduits (not shown) fluidly coupling each of thecompressor 114, the various components of the intake air system 106, andthe intake manifold 108.

The intake air system 106 includes a CAC 118, a CAC bypass line 120, aCAC bypass heater 122, a first control valve 124, a second control valve126, a third control valve 128, a fourth control valve 130, and acontroller 132. In such embodiments, at least one of the first, second,third, and fourth control valves 124, 126, 128, 130 comprises an activecontrol valve that is structured to regulate flow in response to acontrol signal received from the controller 132. In some embodiments, atleast one of the first, second, third, and fourth control valves 124,126, 128, 130 comprises a passive control valve that is structured toregulate flow without the use of an electronic controller. For example,in some embodiments, at least one of the first, second, third, andfourth control valves 124, 126, 128, 130 comprises a press-balancedspring or on-off solenoid to control flow therethrough.

Each of the CAC 118, a CAC bypass line 120, and a CAC bypass heater 122is positioned along the intake air circuit 116 in parallel with theothers. The CAC 118 is structured to cool intake air flowingtherethrough in order to increase charge density, thereby increasingpower output of the engine and preventing knock.

The CAC bypass line 120 is a low-resistance passage that permits intakeair to be transmitted through the intake air circuit 116 without beingtransmitted through the CAC 118.

The CAC bypass heater 122 is structured to heat the intake air flowingtherethrough. According to various embodiments, the CAC bypass heater122 comprises any of an electric grid heater, a gaseous fuel burner, andan engine coolant heat exchanger.

The first control valve 124 is positioned along the intake air circuit116 upstream of the CAC. The first control valve 124 is structured tocontrollably divert the intake air around the CAC 118. The first controlvalve 124 is controllable between an open position, a closed position,and intermediate positions therebetween. When the first control valve124 is in the open position, intake air is directed into the CAC 118.When the first control valve 124 is in the closed position, intake airis directed towards the CAC bypass line 120 and the CAC bypass heater122, and the intake air is blocked from transmission to the CAC 118.Intermediate positions of the first control valve 124 permit acorresponding relative amount of the intake air to be transmitted to theCAC 118.

The second control valve 126 is positioned along the intake air circuit116 upstream of each of the CAC bypass line 120 and the CAC bypassheater 122. The second control valve 126 operates in a similar manner asthe first control valve 124 in that the second control valve 126 iscontrollable between an open position, a closed position, andintermediate positioned therebetween to controllably divert the intakeair around at least one of the CAC bypass line 120 and the CAC bypassheater 122.

The third control valve 128 is positioned along the intake air circuit116 downstream of the CAC. The third control valve 128 is controllablyoperable to selectively block intake air flow from the CAC 118 to theintake manifold 108.

The fourth control valve 130 is positioned along the intake air circuit116 downstream of each of the CAC bypass line 120 and the CAC bypassheater 122. The fourth control valve 130 is controllably operable toselectively block intake air flow from the CAC bypass line 120 or theCAC bypass heater 122.

In some embodiments, the intake air system 106 includes all of thefirst, second, third, and fourth control valves 124, 126, 128, 130, asillustrated in FIG. 1. However, in some embodiments, the intake airsystem 106 includes the first and second control valves 124, 126 anddoes not include the third and fourth control valves 128, 130. In otherembodiments, the intake air system 106 includes only the third andfourth control valves 128, 130 and does not include the first and secondcontrol valves 124, 126.

The controller 132 is communicatively and operatively coupled to each ofthe engine 102; the CAC bypass heater 122; the first, second, third, andfourth control valves 124, 126, 128, 130; and other components of theengine system 100. For example, in some embodiments, the engine system100 also includes an intake manifold temperature sensor 134 operativelycoupled to the intake manifold 108, and to which the controller 132 iscommunicatively and operatively coupled. As described further below inconnection with FIG. 2, the controller 132 is structured to determinevarious operating conditions of the engine system 100, and tocontrollably direct intake air flow through a flow path comprising oneor more of the CAC 118, the CAC bypass line 120, and the CAC bypassheater 122, based on the determined operating conditions, in order tominimize condensation in the intake air system 106. For example, in someembodiments, the determined operating conditions include engine load,ambient temperature, ambient humidity level, charge humidity level, dewpoint, and pressure.

For example, in some embodiments, intake air flow is controllablydirected through a flow path comprising one or more of the CAC 118, theCAC bypass line 120, and the CAC bypass heater 122 based on an intakeair pressure measured upstream of the CAC 118 (e.g., proximate the firstcontrol valve 124). For example, in one embodiment, the first controlvalve 124 is structured to divert flow around the CAC 118 when theintake air pressure is below a predetermined level. In some embodiments,at least one of the first, second, third, and fourth control valves 124,126, 128, 130 is a mechanical (e.g., passive) control valve that ismechanically actuated rather controlled than based on a control signalreceived from the controller 132. For example, in one embodiment, thefirst control valve 124 is controlled based on intake air pressure, suchthat the first control valve 124 diverts flow around the CAC 118 whenthe intake air pressure is below a predetermined level. As the pressureincreases, a spring force on the first control valve 124 is exceeded,causing intake air flow to start transitioning to the CAC 118. In someembodiments, the second control valve is mechanically actuated based onintake air temperature, such that the first control valve 124 divertsair through the CAC bypass heater 122 if the intake air is below apredetermined temperature.

FIG. 2 is a block diagram of the controller 132 of the engine system 100of FIG. 1. The controller 132 includes a processor 202 and memory 204.The memory 204 is shown to include an operating conditions circuit 206,an intake air flow path circuit 208, and a control valve actuationcircuit 210 communicably coupled to each other. In general, thecontroller 132 is structured to control operation of at least one of thefirst, second, third, and fourth control valves 124, 126, 128, 130 basedon determined operating conditions of the engine system 100. Whilevarious circuits with particular functionality are shown in FIG. 2, itshould be understood that the controller 132 may include any number ofcircuits for completing the functions described herein. For example, theactivities of multiple circuits may be combined as a single circuit,additional circuits with additional functionality may be included, etc.Further, it should be understood that the controller 132 may furthercontrol other vehicle activity beyond the scope of the presentdisclosure.

Certain operations of the controller 132 described herein includeoperations to interpret and/or to determine one or more parameters.Interpreting or determining, as utilized herein, includes receivingvalues by any method known in the art, including at least receivingvalues from a datalink or network communication, receiving an electronicsignal (e.g. a voltage, frequency, current, or PWM signal) indicative ofthe value, receiving a computer generated parameter indicative of thevalue, reading the value from a memory location on a non-transientcomputer readable storage medium, receiving the value as a run-timeparameter by any means known in the art, receiving a value by which theinterpreted parameter can be calculated, and/or by referencing a defaultvalue that is interpreted to be the parameter value.

The operating conditions circuit 206 is in operative communication withvarious sensors 212. For example, the sensors 212 may include the intakemanifold temperature sensor 134 (FIG. 1), an ambient temperature sensor,an ambient humidity sensor, a CAC humidity sensor, a dew point sensor, apressure sensor, various engine parameter (e.g., torque) sensors, andother types of sensors. The operating conditions circuit 206 isstructured to receive measurement values from the sensors 212 and tointerpret measurement values based on the received measurement values.The sensors 212 may include any of various types of sensors configuredto measure characteristics related to the engine 102, the turbocharger104, the intake air system 106, and/or related systems. The sensors mayalso include other temperature sensors (e.g., on the engine block,external to the engine 102, in any of the intake air passages, in anexhaust passage, or in any other location), humidity sensors, pressuresensors, an engine speed sensor, an engine torque sensor, a vehiclespeed sensor, a position sensor, etc. Accordingly, the measurementvalues may include, but are not limited to, ambient temperature, engineload (e.g., torque), intake manifold temperature, other intake airtemperatures, engine temperature, coolant temperature, exhausttemperature, turbocharger boost pressure, engine speed, vehicle speed,valve position, and/or any other engine or system characteristics.

Various operating condition values are described herein qualitatively.For example, ambient temperature is described as “cold,” “warm,” and“hot.” However, it should be understood that in practice, thesequalitative descriptors are defined by specific threshold values. Thesespecific threshold values can vary based on several factors, such asengine displacement, power, application, etc. Table 1 below providesalternative definitions of the operating condition values describedherein in terms of threshold values.

TABLE 1 Intake Air Flow Path Conditions Ambient Cold Cold/Warm Warm/HotTemperature At or Below 1^(st) Between 1^(st) and 2^(nd) At or above2^(nd) Temp Threshold Temp Threshold Temp Threshold Value Values ValueEngine Load Light Load Partial Load Partial/Full Load At or Below 1^(st)Between 1^(st) and 2^(nd) At or above 2^(nd) Torque Threshold TorqueThreshold Torque Value Values Threshold Value Flow Through None PartialMajority Intake Air ≤5% 1-99% ≥50% System Substantially All AllComponents ≥90% ≥95% (% of Total Mass Flow)

The intake air flow path circuit 208 is structured to determine, basedon the measurement signals received by the operating conditions circuit206, a desired flow path of the intake air through at least one of thecharge air cooler 118, the CAC bypass line 120, and the CAC bypassheater 122. As explained in further detail below, the intake air flowpath can depend on various operating conditions, such as ambienttemperature, engine load, and intake manifold temperature, among otherfactors. Depending on the particular operating conditions, the intakeair flow path circuit 208 can determine the intake air flow path eitherstatically or dynamically throughout operation within the operatingconditions defining a particular intake air flow path.

The control valve actuation circuit 210 is in operative communicationwith the intake air flow path circuit 208, and with each of the first,second, third, and fourth control valves 124, 126, 128, 130 of theintake air system 106 of FIG. 1. The control valve actuation circuit 210is structured to control operation of one or more of the first, second,third, and fourth control valves 124, 126, 128, 130 based on the desiredflow path determined by the intake air flow path circuit 208.

At cold ambient temperatures and light engine load (e.g., idle)conditions, the intake air flow path circuit 208 is structured to definea first intake air flow path so as to direct substantially all of theintake air flow through the CAC bypass heater 122, and to prevent flowthrough each of the CAC 118 and the CAC bypass line 120. The firstintake air flow path is maintained through the CAC bypass heater 122 fora period of time after a cold start of the engine 102. In one exampleimplementation, the control valve actuation circuit 210 is structured toclose each of the first and second control valves 124, 126 to controlintake air flow through the first intake air flow path.

At cold ambient temperatures and partial load conditions, the intake airflow path circuit 208 is structured to define a second intake air flowpath so as to direct intake air flow in part through the CAC bypassheater 122 and in part through the CAC bypass line 120, and to preventflow through the CAC 118. Intake air temperature (e.g., intake manifoldtemperature) is measured and monitored (e.g., via the operatingconditions circuit 206) during operation of the engine 102 under theseconditions. In some implementations, the intake air flow path circuit208 is structured dynamically determine the second intake air flow pathto divide flow (e.g., define flow percentages) between each of the CACbypass heater 122 and the CAC bypass line 120 so as to maintain theintake air temperature above a threshold value (e.g., its dew point).According to various embodiments, the second intake air flow path caninclude directing up to substantially all of the intake air flow throughthe CAC bypass heater 122. In one example implementation, the controlvalve actuation circuit 210 is structured to close the first controlvalve 124 and to controllably and dynamically actuate the second controlvalve 126 between partially closed and fully closed positions to controlintake air flow through the second intake air flow path.

At cold to warm ambient temperatures and/or partial engine loadconditions, the intake air flow path circuit 208 is structured to definea third intake air flow path to maintain air flow in part through theCAC bypass heater 122 and in part through the CAC bypass line 120, andto prevent flow through the CAC 118. The intake air flow path circuit208 is structured to dynamically determine the third intake air flowpath in a similar manner as with the second intake air flow path.According to various embodiments, the third intake air flow path caninclude directing up to substantially all of the intake air flow throughthe CAC bypass line 120 so as to minimize the air flow restrictions ofthe CAC bypass heater 122. In one example implementation, the controlvalve actuation circuit 210 is structured to close the first controlvalve 124 and to controllably and dynamically actuate the second controlvalve 126 between partially open and fully open positions to controlintake air flow through the third intake air flow path.

At warm to hot ambient temperatures, and/or partial to full engine loadconditions, the intake air flow path circuit 208 is structured to definea fourth intake air flow path so as to direct intake air flow at leastpartially through the CAC 118, and to block intake air flow through theCAC bypass heater 122. According to various embodiments, the fourthintake air flow path can include directing a majority and up tosubstantially all of the intake air flow through the CAC 118 so as tomaximize charge air cooling. In one example implementation, the controlvalve actuation circuit 210 is structured to open the first controlvalve 124 and to close the second control valve 126 to control intakeair flow through the fourth intake air flow path.

TABLE 2 Intake Air Flow Path Conditions Flow Flow Intake through throughAir Flow CAC CAC Flow Ambient Engine through bypass bypass PathTemperature Load CAC line heater 1 Cold Light None None All Load 2 ColdPartial None Partial Partial (Up to Load Substantially All) 3 Cold/WarmPartial None Partial (Up to None-Partial Load Substantially All) 4Warm/Hot Partial/ Majority to Partial to None Full All None Load

FIG. 3 is a block diagram of a high-efficiency SI LPG engine system 300,according to an example embodiment. Certain features of the enginesystem 300 of FIG. 3 are similar to those of the engine system 100 ofFIG. 1. However, the engine system 300 includes various features inaddition to those described in connection with the engine system 100 ofFIG. 1.

The engine system 300 includes an engine 302, first and secondturbochargers 304, 305, an intake air system 306, and an exhaust system307. The engine 302 is structured to operate using LPG as its single andsole fuel source. The engine 302 receives LPG from one or more LPG tanks309 fluidly coupled to the engine 302 via operation of a fuel pump 311.Other engines systems that utilize propane typically utilize propane ingaseous form, and/or utilize propane in conjunction with other fuels. Incontrast, the engine 302 is specifically designed and optimized tooperate using only LPG. In some embodiments, the engine 302 isstructured to operate using a stoichiometric air/fuel ratio. However, inother embodiments, the engine 302 is structured to operate using a leanair/fuel ratio. In some implementations, the air/fuel ratio of theengine 302 is selected depending on the target market. In theseimplementations, the air/fuel ratio does not switch across the operatingspace. Combustion of the LPG is controlled via an ignition module 313operatively coupled to a controller 332. According to variousembodiments, the ignition module 313 is structured to operate any ofvarious types of ignition systems, such as standard spark plugs withhigh-energy ignition (“HEI”), passive pre-chamber, fuel-fed pre-chamber,or laser ignition.

In some embodiments, the engine 302 includes a cooling system (not shownin FIG. 3) structured to facilitate evaporative cooling using the LPGfuel. In other words, the same fuel that is used to power the engine 302is also used to provide evaporative cooling for the engine 302.

The engine 302 includes an intake manifold 308 and a front and rearexhaust manifolds 310, 315. The front and rear exhaust manifolds 310,315 are parts of a split exhaust manifold. The intake manifold 308 isfluidly and operatively coupled to the intake air system 306. The intakemanifold 308 is structured to transmit intake air received from theintake air system 306 to cylinders of the engine 302. The front and rearexhaust manifolds 310, 315 are structured to retrieve exhaust gas fromthe cylinders after the air/fuel mixture is combusted, and to transmitthe exhaust gas to the exhaust system 307 for aftertreatment.

The first turbocharger 304 includes a first turbine 312 and a firstcompressor 314, which are mounted on a common shaft (not shown). Thefirst turbine 312 is in exhaust gas receiving communication with thefront exhaust manifold 310. The exhaust gas received from the frontexhaust manifold 310 causes rotation of the first turbine 312, which inturn causes rotation of the first compressor 314. The first compressor314 receives filtered fresh intake air upon actuation of a first inletthrottle 317, and compresses the intake air to increase its chargedensity. In some embodiments, the first inlet throttle 317 is positionedupstream of the first compressor 314. However, in other embodiments, thefirst inlet throttle 317 is positioned downstream of the firstcompressor 314. The first compressor 314 provides the compressed intakeair to the intake air system 306.

The second turbocharger 305 similarly includes a second turbine 319 anda second compressor 321. The second turbine 319 is in exhaust gasreceiving communication with the rear exhaust manifold 315. The secondturbocharger 305 operates in a similar manner as the first turbocharger304, and also provides compressed intake air to the intake air system306. For example, the second compressor 321 receives filtered freshintake air upon actuation of a second inlet throttle 323, and compressesthe intake air to increase its charge density. In some embodiments, thesecond inlet throttle 323 is positioned downstream of the secondcompressor 321. However, in other embodiments, the second inlet throttle323 is positioned downstream of the second compressor 321. Each of thefirst and second turbochargers 304, 305 include independently operablewastegates (not shown).

The intake air system 306 includes an intake air circuit 316, a CAC 318,a CAC bypass line 320, a CAC bypass heater 322, a first control valve324, a second control valve 326, a third control valve 328, a fourthcontrol valve 330, and the controller 332. The intake air system 306operates in a generally similar manner to the intake air system 106 ofFIG. 1. For example, the controller 332 is structured to determinevarious operating conditions of the engine system 300, and tocontrollably direct intake air flow through a flow path comprising oneor more of the CAC 318, the CAC bypass line 320, and the CAC bypassheater 322, based on the determined operating conditions, in order tominimize condensation in the intake air system 306.

The exhaust system 307 includes first and second aftertreatment devices334, 336 and an exhaust throttle 338. Exhaust gas is transmitted fromthe front and rear exhaust manifolds 310, 315 to the respective firstand second turbines 312, 319, and through the first and secondaftertreatment devices 334, 336. The first aftertreatment device 334 isa “closely coupled” aftertreatment device because it is positionedrelatively close to the engine 302. The position of the firstaftertreatment device 334 close to the engine 302 minimizes temperaturelosses of the exhaust gas before it reaches the first aftertreatmentdevice 334. Each of the first and second aftertreatment devices 334,336, according to various embodiments, include one or more of anoxidation catalyst, a three-way catalyst, a particulate filter, aselective catalytic reduction catalyst, a storage device, or any ofvarious other types of aftertreatment devices.

The engine system 300 also includes an EGR system 340. The EGR system340 is structured to transmit a portion of the exhaust gas from theengine 302 back to the intake manifold 308 of the engine 302. Operationof the EGR system 340 reduces nitrogen oxide (NO_(x)) emissions from theengine 302. In some embodiments, the EGR system 340 receives exhaust gasfrom the exhaust system 307 downstream of the first aftertreatmentdevice 334 and upstream of the second aftertreatment device 336. Inother embodiments, the EGR system 340 receives exhaust gas from theexhaust system 307 downstream of at least one of the first and secondturbochargers 304, 305, and upstream of the first aftertreatment device334. The amount of exhaust gas that is recirculated through the EGRsystem 340 is controlled via operation of the exhaust throttle 338. Flowthrough the EGR system 340 is also controlled via operation of an EGRvalve 341. Some embodiments do not include at least one of the exhaustthrottle 338 and the EGR valve 341. It should be understood that,according to various embodiments, the EGR system 340 may be controlledvia active control elements, passive control elements, or a combinationof active and passive control elements. The EGR system 340 illustratedin FIG. 3 is a low-pressure EGR system because it recirculates exhaustgas from downstream of the first and second turbochargers 304, 305. Insome embodiments, the engine system 300 also includes a high-pressureEGR system, which circulates exhaust gas from upstream of the first andsecond turbochargers 304, 305. The exhaust gas recirculated through theEGR system 340 is mixed with the intake air via an EGR mixer 342, andsubsequently transmitted to the intake manifold 308 of the engine 302.

FIG. 4 is a block diagram of a high-efficiency SI LPG engine system 400including the engine 302 of FIG. 3, according to an alternative exampleembodiment. The engine system 400 of FIG. 4 is generally similar to theengine system 300 of FIG. 3. However, the engine system 400 of FIG. 4includes a single wastegated turbocharger 402 with a turbine 404comprising a divided turbine housing. In particular, the turbine 404includes a first housing section 406 and a second housing section 408.The first housing section 406 is structured to receive exhaust gas fromthe front exhaust manifold 310, and the second housing section 408 isstructured to receive exhaust gas from the rear exhaust manifold 315.

The divided turbine housing of the turbocharger 402 and the splitexhaust manifold including the front and rear exhaust manifolds 310, 315operate to minimize or prevent combustion knock. In particular, thedivided housing of the turbocharger 402 prevents cross-talk(backpressure) between cylinders. The divided housing of theturbocharger 402 also eliminates pumping overlap (backpressure) betweencylinders.

It should be understood that no claim element herein is to be construedunder the provisions of 35 U.S.C. § 112(f), unless the element isexpressly recited using the phrase “means for.” The schematic flow chartdiagrams and method schematic diagrams described above are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of representative embodiments. Other steps,orderings and methods may be conceived that are equivalent in function,logic, or effect to one or more steps, or portions thereof, of themethods illustrated in the schematic diagrams. Further, referencethroughout this specification to “one embodiment,” “an embodiment,” “anexample embodiment,” or similar language means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in one embodiment,” “in anembodiment,” “in an example embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment.

Additionally, the format and symbols employed are provided to explainthe logical steps of the schematic diagrams and are understood not tolimit the scope of the methods illustrated by the diagrams. Althoughvarious arrow types and line types may be employed in the schematicdiagrams, they are understood not to limit the scope of thecorresponding methods. Indeed, some arrows or other connectors may beused to indicate only the logical flow of a method. For instance, anarrow may indicate a waiting or monitoring period of unspecifiedduration between enumerated steps of a depicted method. Additionally,the order in which a particular method occurs may or may not strictlyadhere to the order of the corresponding steps shown. It will also benoted that each block of the block diagrams and/or flowchart diagrams,and combinations of blocks in the block diagrams and/or flowchartdiagrams, can be implemented by special purpose hardware-based systemsthat perform the specified functions or acts, or combinations of specialpurpose hardware and program code.

Many of the functional units described in this specification have beenlabeled as circuits, in order to more particularly emphasize theirimplementation independence. For example, a circuit may be implementedas a hardware circuit comprising custom very-large-scale integration(VLSI) circuits or gate arrays, off-the-shelf semiconductors such aslogic chips, transistors, or other discrete components. A circuit mayalso be implemented in programmable hardware devices such as fieldprogrammable gate arrays, programmable array logic, programmable logicdevices or the like.

As mentioned above, circuits may also be implemented in machine-readablemedium for execution by various types of processors, such as theprocessor 202 of FIG. 2. An identified circuit of executable code may,for instance, comprise one or more physical or logical blocks ofcomputer instructions, which may, for instance, be organized as anobject, procedure, or function. Nevertheless, the executables of anidentified circuit need not be physically located together, but maycomprise disparate instructions stored in different locations which,when joined logically together, comprise the circuit and achieve thestated purpose for the circuit. Indeed, a circuit of computer readableprogram code may be a single instruction, or many instructions, and mayeven be distributed over several different code segments, amongdifferent programs, and across several memory devices. Similarly,operational data may be identified and illustrated herein withincircuits, and may be embodied in any suitable form and organized withinany suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.

The computer readable medium (also referred to herein asmachine-readable media or machine-readable content) may be a tangiblecomputer readable storage medium storing the computer readable programcode. The computer readable storage medium may be, for example, but notlimited to, an electronic, magnetic, optical, electromagnetic, infrared,holographic, micromechanical, or semiconductor system, apparatus, ordevice, or any suitable combination of the foregoing. As alluded toabove, examples of the computer readable storage medium may include butare not limited to a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), a portable compact discread-only memory (CD-ROM), a digital versatile disc (DVD), an opticalstorage device, a magnetic storage device, a holographic storage medium,a micromechanical storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, and/or storecomputer readable program code for use by and/or in connection with aninstruction execution system, apparatus, or device.

Computer readable program code for carrying out operations for aspectsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages.

The program code may also be stored in a computer readable medium thatcan direct a computer, other programmable data processing apparatus, orother devices to function in a particular manner, such that theinstructions stored in the computer readable medium produce an articleof manufacture including instructions which implement the function/actspecified in the schematic flowchart diagrams and/or schematic blockdiagrams block or blocks.

Accordingly, the present disclosure may be embodied in other specificforms without departing from its spirit or essential characteristics.The described embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the disclosure is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. An intake air system, comprising: a turbochargercomprising a compressor; an intake air circuit structured to transmitintake air from the compressor to an intake manifold of an engine; acharge air cooler positioned along the intake air circuit; a bypass linepositioned along the intake air circuit in parallel with the charge aircooler; a bypass heater positioned along the intake air circuit inparallel with each of the charge air cooler and the bypass line; a firstvalve positioned along the intake air circuit upstream of the charge aircooler, the first valve structured to controllably divert the intake airaround the charge air cooler; and a second valve positioned along theintake air circuit upstream of the bypass heater, the second valvestructured to controllably divert the intake air around at least one ofthe bypass line and the bypass heater.
 2. The intake air system of claim1, wherein the first valve is a first control valve and the second valveis a second control valve, and further comprising: a controlleroperatively coupled to each of the engine, the first control valve, andthe second control valve, the controller comprising: an operatingconditions circuit structured to: receive an engine load signalindicative of an engine load on the engine; and receive an ambienttemperature signal indicative of a measured ambient temperature externalto the engine; an intake air flow path circuit structured to determine,based on each of the engine load signal and the ambient temperaturesignal, a desired flow path of the intake air through at least one ofthe charge air cooler, the bypass line, and the bypass heater; and acontrol valve actuation circuit structured to control each of the firstand second control valves to cause the intake air to flow along thedetermined desired flow path.
 3. The intake air system of claim 2,wherein the intake air flow path circuit is structured to, in responseto the engine load being less than a first engine load value and theambient temperature is less than a first ambient temperature value,determine that the desired flow path of the intake air includesdirecting flow of the intake air through the bypass heater and divertingflow of the intake air around each of the charge air cooler and thebypass line.
 4. The intake air system of claim 1, wherein the firstvalve is structured to controllably divert the intake air around thecharge air cooler when a pressure of the intake air proximate the firstvalve is less than a first intake air pressure level.
 5. The intake airsystem of claim 4, wherein the first valve is a mechanically-controlledvalve.
 6. A method, comprising: providing an intake air system for anengine, the intake air system comprising: an intake air circuitstructured to transmit intake air from a compressor to an intakemanifold of the engine, a charge air cooler positioned along the intakeair circuit, a first bypass line positioned along the intake air circuitin parallel with the charge air cooler, a second bypass line positionedalong the intake air circuit in parallel with each of the charge aircooler and the first bypass line, the second bypass line including abypass heater; determining engine operating conditions; and selectivelydirecting intake air flow through at least one of the charge air cooler,the first bypass line, and the second bypass line so as to maintain atemperature of the intake air flow above a dew point temperature.
 7. Aspark-ignited liquid propane gas engine system, comprising: aspark-ignited internal combustion engine structured to operate usingliquid propane gas as its sole fuel source; and an air handling systemoperatively coupled to the engine, the air handling system comprising: afirst turbocharger comprising a first turbine in exhaust gas receivingcommunication with a first exhaust manifold of the engine, and a firstcompressor in intake air providing communication with an intake aircircuit; a second turbocharger comprising a second turbine in exhaustgas receiving communication with a second exhaust manifold of theengine, and a second compressor in intake air providing communicationwith the intake air circuit; a charge air condensation reduction systemcomprising a charge air cooler, a bypass line, and a bypass heater, eachof the charge air cooler, the bypass line, and the bypass heaterpositioned along the intake air circuit in parallel with the others; andan intake air flow control system structured to controllably directintake air flow through a flow path comprising one or more of the chargeair cooler, the bypass line, and the bypass heater in order to minimizecondensation in the intake air circuit, wherein the intake air circuitis structured to transmit the intake air from the charge aircondensation reduction system to an intake manifold of the engine. 8.The engine system of claim 7, wherein the engine is structured tooperate using a piston compression ratio of at least 13.0:1.
 9. Theengine system of claim 7, further comprising: a liquid propane gas fueltank structured to store liquid propane gas; and a direct fuel injectionsystem in liquid propane gas receiving communication with the fuel tankand in liquid propane gas providing communication with each of aplurality of cylinders of the engine.
 10. A spark-ignited liquid propanefuel engine system, comprising: a spark-ignited internal combustionengine structured to operate using liquid propane fuel as its sole fuelsource; a direct fuel injection system in liquid propane fuel providingcommunication with each of a plurality of cylinders of the engine; and aturbocharger comprising a turbine in exhaust gas receiving communicationwith an exhaust manifold of the engine, and a compressor in intake airproviding communication with an intake manifold of the engine; a chargeair cooler in intake air receiving communication with the compressor,the compressor in intake air providing communication with an intake aircircuit, the charge air cooler positioned along the intake air circuit,the intake air circuit further defining a bypass line in parallel withthe charge air cooler; and a bypass heater positioned along the intakeair circuit in parallel with each of the charge air cooler and thebypass line.
 11. The engine system of claim 10, wherein the engine isstructured to operate using a piston compression ratio of at least13.0:1.
 12. The engine system of claim 11, further comprising an exhaustgas recirculation system in exhaust gas receiving communication with theexhaust manifold and in exhaust gas providing communication with theintake manifold.
 13. The engine system of claim 11, wherein the enginesystem does not include an exhaust gas recirculation system in exhaustgas receiving communication with the exhaust manifold and in exhaust gasproviding communication with the intake manifold.
 14. The engine systemof claim 11, wherein the turbocharger is a first turbocharger, theturbine is a first turbine, and the compressor is a first compressor,and wherein the engine system further comprises: a second turbochargercomprising a second turbine in exhaust gas receiving communication withthe exhaust manifold, and a second compressor in intake air providingcommunication with the intake manifold.
 15. The engine system of claim14, wherein the exhaust manifold is a split exhaust manifold comprising:a front exhaust manifold portion in exhaust gas providing communicationwith the first turbine; and a rear exhaust manifold portion in exhaustgas providing communication with the second turbine.
 16. The enginesystem of claim 11, further comprising the charge air cooler in intakeair providing communication with the intake manifold.
 17. The enginesystem of claim 10, further comprising an intake air flow control systemstructured to controllably direct intake air flow through a flow pathcomprising one or more of the charge air cooler, the bypass line, andthe bypass heater in order to minimize condensation in the intake aircircuit.
 18. The engine system of claim 17, wherein the intake air flowcontrol system comprises: a first valve positioned along the intake aircircuit upstream of the charge air cooler, the first valve structured tocontrollably divert the intake air around the charge air cooler; and asecond valve positioned along the intake air circuit upstream of thebypass heater, the second valve structured to controllably divert theintake air around at least one of the bypass line and the bypass heater.